This month NADIS vet Richard Laven writes for South West Farmer on the prevention of husk in cattle. NADIS (National Animal Disease Information Service) is a network of 40 veterinary practices and six veterinary colleges monitoring diseases in cattle, sheep and pigs in the UK. NADIS is sponsored by the Meat and Livestock Commission, Elanco Animal Health and Intervet.

NADIS data shows that outbreaks of husk tend to begin in June, increasing to a peak in September/October. The number of outbreaks per month falls during the autumn, although cases continue until January.

Although lungworm is often thought of as a disease of youngstock, it is now also a significant problem in adult cattle. In recent years around half of all reported outbreaks occurred in adult cattle. Husk primarily affects animals at grass from mid-summer to autumn because the number of infective larvae on the grass is then at its peak. However, the warmer wetter autumns and winters now mean that the larvae are active on the pasture for longer and consequently severe cases of husk now being noted in November and December.

Treatment Early treatment is essential and modern wormers are effective. Antibiotics are also required if severely affected. Treat all cattle in a group at the same time.

Prevention Lungworm infection is considerably less predictable than that of the gut worms. We do not fully understand exactly how lungworm larvae survive in the environment and how they are transmitted from cow to cow.

However, there are two major factors that rapidly increase the spread of the disease:

1 Lungworm larvae, not eggs, are found in the dung and become infective for other cattle much more rapidly than worms whose eggs hatch outside the cattle. Wet weather is also associated with much greater spread of larvae.

2 The fungus Pilobolus in cow pats can spread larvae long distances along with its spores. Earthworms or dung beetles may also be involved. This means that lungworm will not be controlled by a dose and move strategy. The unpredictability and rapid build-up of larvae mean that strategies which control gut worms are ineffective. Thus, there are two strategies for controlling lungworm: 1 Vaccination This is the best, most effective method of control and on farms with previous history of husk, should be a priority. The vaccine is a live vaccine, made from irradiated larvae which are incapable of causing disease.

For dairy-type calves, vaccination should be completed at least two weeks before turnout, for suckled calves it should finish two weeks before the calves begin to eat significant amounts of grass. Wormers should not be given until two weeks after the final dose of vaccine. The vaccine produces very good immunity but does not prevent all worms from natural infections completing their life cycle. This means that, even after vaccination, there may still be a very low level of larvae on the pasture. If all youngstock are not vaccinated, larvae numbers can increase very rapidly, leading to disease in the unvaccinated animals.

2 Suppression with Regular Worming Vaccination should not be given to calves showing signs of lung damage (from any cause) as it may make the disease significantly worse. In such cases, regular worming can prevent disease. This method can also be used in healthy calves, and many manufacturers have developed regimes for their wormers that can control husk. However, if the worming regime is too effective then the cattle will not become naturally immune to lungworm, and can then develop husk in their second or even third grazing season. This may be the major reason for the increase in outbreaks of adult husk. The effect is most commonly seen with sustained-release boluses containing ivermectin. Repeat dose strategies using avermectins and boluses containing oxfendazole have been shown to allow immunity to develop. All cases of suspected lungworm in adult cattle should be referred to a veterinarian.